In an elevator, for example a passenger elevator in a building, the automatic elevator doors are routinely monitored in respect of whether an object is situated in their movement path. If this is the case, the door is not closed, in order that a collision, for example with a person, cannot occur. Under normal conditions, this is certainly a correct approach. In the case of a fire, however, serious problems can occur since no distinction is made between smoke and an object. The following scenario can arise:                An elevator stops at a floor where there is a fire. The door opens and smoke enters the elevator car. People in the lift would like to leave this floor again as rapidly as possible. This is not possible, however, since the door sensor identifies the smoke as an object and therefore does not permit a control to the effect that the elevator doors close. People have already died in such a situation.        
British Patent Application No. GB 23 15 134 A discloses an elevator door control system in which the elevator doors are not closed if an object is detected by a series of sensors. However, the closure suspension function is inhibited if smoke is detected by a further sensor. This enables the doors to be closed even though the series of sensors per se detects an object, if the smoke sensor detects smoke.
Such an embodiment is comparatively complex and costly.